In recent years, an organic photovoltaic cell having an organic semiconductor film has been examined due to simplification of a manufacturing process. Since an organic semiconductor thin film can be formed by a coating method, simplification of a process of manufacturing a photovoltaic cell and a reduction in power generation cost are expected.
There has been known an organic photovoltaic cell having a bulk hetero junction type photoelectric conversion active layer. In the bulk hetero junction type photoelectric conversion active layer, an electron donating organic semiconductor (p-type organic semiconductor) and an electron accepting organic semiconductor (n-type organic semiconductor) are mixed, so that the bulk hetero junction type photoelectric conversion active layer has a large area of a pn junction interface where charge separation occurs.
When the bulk hetero junction type photoelectric conversion active layer is formed by a coating method, a coating solution containing a p-type organic semiconductor, an n-type organic semiconductor, and a solvent is used as a main component. In order to form a photoelectric conversion active layer excellent in power conversion efficiency, an alkane compound whose end is halogen-substituted (for example, 1,8-diiodooctane) is added to the coating solution.
In many cases, power conversion efficiency of a photovoltaic cell decreases as the photovoltaic cell is used. That is, the photovoltaic cell which power conversion efficiency significantly decreases during use is far to be practical, even though its power conversion efficiency is high immediately after manufacture.